The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Uber drivers seek disclosure before trial

Twenty Uber drivers are challenging a decision by the West Australian Department of Transport not to disclose documents they believe may help them defend accusations of operating illegally.

Sukhwinder Singh previously pleaded not guilty to two counts of using a vehicle as a taxi without authorisation and one count of interfering with a surveillance unit in a taxi.

The 19 other men have been charged with failing to comply with a lawful direction of an authorised officer.

The department claimed in the Perth Magistrates Court on Monday that there was "public interest immunity" over the documents because they commented on department operations and were not relevant to the trial.

But a lawyer for the accused men said a trial date could not be set until the legal issue was resolved.